Most electrical power generation in the United States relies on non-renewable fossil fuels such as coal, oil, and natural gas, which are harmful to the environment and increasingly costly. Generating power from renewable sources, such as solar and wind energy, avoids the increasing cost and environmental harm associated with fossil fuels.
Residential power customers can reduce power bills significantly by generating some of their own electricity from renewable sources. However, installing a large array of solar panels or a windmill may involve a large upfront investment, which may be paid off by reduced power bills only over several years (if at all, depending on the cost and the lifespan of the solar panels or windmill). Also, solar energy and wind energy are highly variable, and may provide little power on overcast or calm days. Moreover, some cities and homeowner associations don't allow homeowners to install large arrays of solar panels, or a large windmill.